I've taken the tandem idea a little further, even in the majors. I've got 2 stud setup guys with 40+ stamina and 90+ durability. Either would make elite "Mr. Maagic Closers", but I use both as tandem B starters. It takes active managing, but one is a tandem 3A and the other a tandem 4A. I reduce the pitch counts of my 4 starters and actively rotate them through the 3A and 4A slots. Halfway through the season, both guys are on pace for 180-200 innings, along with the same amount for the 4 starters. One of my LR relievers can be spot-started (which sometimes becomes necessary with extra inning games or if one guy gets lit up a time or two) and the rest of the pen is solid.
I also do not use a 'closer' on any of my ML teams. I don't care how many "saves" anyone gets. I fail to see the same value in holding a 3-run lead in one inning pitched versus holding a tie game for 2-3 innings. Of course that's probably why one of my Tandem B relievers is on pace for 24 wins (another stat that doesn't mean as much individually).
As far as the original quesion, if you want your prospect to develop, maximize his innings and expose him to good coaching. His stats won't matter at all.